feat: day 9 part 2 complete

day9/main.py

@@ -1,4 +1,5 @@
 import time
+from os import system, name
 
 moves = []
 
@@ -9,31 +10,36 @@ for line in lines:
     line = line.strip()
     moves.append((line[0], int(line.split(" ")[-1])))
 
+# Part 1
+
 head = (0, 0)
 tail = (0, 0)
 visited_positions = {tail}
 
 
-def get_tails_new_pos(head, tail):
+def get_knot_new_pos(front_knot, knot):
-    x_diff = head[0] - tail[0]
+    x_diff = front_knot[0] - knot[0]
-    y_diff = head[1] - tail[1]
+    y_diff = front_knot[1] - knot[1]
 
     if abs(x_diff) <= 1 and abs(y_diff) <= 1:
-        return tail
+        return knot
 
-    new_x = tail[0]
+    new_x = knot[0]
-    new_y = tail[1]
+    new_y = knot[1]
 
-    if abs(x_diff) > 1 and abs(y_diff) >= 1:
+    if abs(x_diff) > 1 and abs(y_diff) > 1:
-        new_x = tail[0] + x_diff // 2
+        new_x = knot[0] + x_diff // 2
-        new_y = tail[1] + y_diff
+        new_y = knot[1] + y_diff // 2
+    elif abs(x_diff) > 1 and abs(y_diff) >= 1:
+        new_x = knot[0] + x_diff // 2
+        new_y = knot[1] + y_diff
     elif abs(y_diff) > 1 and abs(x_diff) >= 1:
-        new_y = tail[1] + y_diff // 2
+        new_y = knot[1] + y_diff // 2
-        new_x = tail[0] + x_diff
+        new_x = knot[0] + x_diff
     elif abs(x_diff) > 1:
-        new_x = tail[0] + x_diff // 2
+        new_x = knot[0] + x_diff // 2
     elif abs(y_diff) > 1:
-        new_y = tail[1] + y_diff // 2
+        new_y = knot[1] + y_diff // 2
 
     return (new_x, new_y)
 
@@ -49,8 +55,54 @@ for move in moves:
         elif move[0] == "L":
             head = (head[0], head[1] - 1)
 
-        tail = get_tails_new_pos(head, tail)
+        tail = get_knot_new_pos(head, tail)
 
         visited_positions.add(tail)
 
 print("Part 1: " + str(len(visited_positions)))
+
+# Part 2
+
+head = (0, 0)
+knots = [(0, 0) for _ in range(1, 10)]
+
+
+def print_grid():
+    system('clear')
+    for x in range(-10, 10):
+        for y in range(-10, 10):
+            to_print = "."
+            if (-x, y) == (0, 0):
+                to_print = "s"
+            if (-x, y) in knots:
+                to_print = str(knots.index((-x, y)) + 1)
+            if (-x, y) == head:
+                to_print = "H"
+            print(to_print, end="")
+        print()
+
+
+visited_positions = {knots[-1]}
+for move in moves:
+    for _ in range(move[1]):
+        if move[0] == "U":
+            head = (head[0] + 1, head[1])
+        elif move[0] == "D":
+            head = (head[0] - 1, head[1])
+        elif move[0] == "R":
+            head = (head[0], head[1] + 1)
+        elif move[0] == "L":
+            head = (head[0], head[1] - 1)
+
+        for i in range(len(knots)):
+            # for debugging purposes
+            # print_grid()
+            # input("_")
+            if i == 0:
+                knots[i] = get_knot_new_pos(head, knots[i])
+            else:
+                knots[i] = get_knot_new_pos(knots[i - 1], knots[i])
+
+        visited_positions.add(knots[-1])
+
+print("Part 2: " + str(len(visited_positions)))

input.txt

@@ -1,8 +0,0 @@
-R 4
-U 4
-L 3
-D 1
-R 4
-D 1
-L 5
-R 2